subract.js

/*
* Question:
*  Subtract given two positive integer as string without using `atoi` or number parser `parseInt, parseFloat` and return signed integer as string.
* Data types:
*  - function subtract(num1: unsigned integer as String, num2: unsigned integer as string) : signed integer as string
* Rules:
*  - Don't use atoi or parseInt for inputs directly
* Duration:
*  - 45 minutes
* Examples:
*  - subtract('1000', '10000') //-9000
*  - subtract("123", '123') // 0
*  - subtract('336651231281827315348592312318953984723125348123', '1') //336651231281827315348592312318953984723125348122
* Submission:
*  Please share your code on a public platform and send access link to alperen@base64.ai via email.
 */

let subtract = (num1,num2) => {
  if (num1 == num2)
    return '0';


  const isSmall = (n1, n2) => {
    const n1len = n1.length;
    const n2len = n2.length;

    if (n1len > n2len)
      return false;
    else if (n1len < n2len)
      return true;
    
    for (let i = 0; i < n1len; i++) {
      if (n1[i] < n2[i])
        return true;
      else if (n1[i] > n2[i])
        return false;
    }

    return false;
  };

  debugger;

  let big = isSmall(num1, num2) ? num2 : num1;
  let small = isSmall(num1, num2) ? num1 : num2;
  let biglen = big.length;
  let smalllen = small.length;

  big = big.split('').reverse().join("")
  small = small.split('').reverse().join("")

  const realDiff = [];

  for (let i = 0; i < smalllen; i++) {
    let diff = big[i] - small[i];
    
    // elde al
    if (diff < 0) {
      let foo = parseInt(big[i+1]) - 1;
      for (let j = i+1; foo < 0; j++) {
        foo = parseInt(big[j]) - 1;

        if (foo >= 0) {
          let tmp = big.split('');
          tmp[j] = foo;
          big = tmp.join('')
        }
      }
      if (isNaN(foo)) {
        diff = 0;
      }
      else {
        diff = parseInt(big[i]) + 10 - small[i];
      }


      realDiff.push(diff);
    }
    else {
      realDiff.push(diff);
    }
  }

  if (big.replace(/0/g, '') === '') {
    for (let i = 1; i < biglen - smalllen; i++) {
      realDiff.push(9);
    }
  }

  realDiff.push(big.slice(smalllen, biglen));

  return realDiff.reverse().join('');
}

console.log(subtract('1000', '10000'),subtract('1000', '10000') === '-9000')
console.log(subtract('123', '123'),subtract('123', '123') === '0')
console.log(subtract('336651231281827315348592312318953984723125348123', '1'),
  subtract('336651231281827315348592312318953984723125348123', '1') === '336651231281827315348592312318953984723125348122')